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International Journal of Mining Science and Technology xxx (2016) xxx–xxx

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International Journal of Mining Science and Technology

journal homepage: www.elsevier .com/locate / i jmst

Statistical analysis and concentration of iron ore using Longi LGS 500WHIMS

http://dx.doi.org/10.1016/j.ijmst.2016.05.0522095-2686/� 2016 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

⇑ Corresponding author. Tel.: +27 11 709 4366.E-mail address: [email protected] (M.J. Makhula).

Please cite this article in press as: Makhula MJ et al. Statistical analysis and concentration of iron ore using Longi LGS 500 WHIMS. Int J Min Sci T(2016), http://dx.doi.org/10.1016/j.ijmst.2016.05.052

Makhula M.J. a,b,⇑, Falcon R.M.S. b, Bergmann C.P. a, Bada S.O. b

aDepartment of Mineral Processing Division, Mintek, Johannesburg 2125, South Africab School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg 2050, South Africa

a r t i c l e i n f o

Article history:Received 1 December 2015Received in revised form 28 February 2016Accepted 1 April 2016Available online xxxx

Keywords:Magnetic separationLongi LGS 500HematiteANOVA

a b s t r a c t

A Longi LGS 500 wet high intensity magnetic separator (WHIMS) was used to concentrate a fine, lowgrade South African hematite ore. The ore was prepared into different size fractions and was subjectedto changes in pulp density, magnetic field intensity and pulsation frequency which followed a 33 full fac-torial matrix. The concentrate mass yield and Fe grade were selected as the dependent responses to thechanges. The analysis of variance (ANOVA) shows that the variables investigated are significant to thematerial’s response to magnetic separation. This significance was in the order of magnetic field intensityfollowed by pulsation frequency and then pulp density. It was also noted that a single stage magneticseparation has a potential to upgrade a feed (�75 lm and 40% Fe) to a 55% Fe grade, as the pulsation fre-quency increases. In addition, the model predictions and actual data were in good agreement, reportingregression coefficients within acceptable ranges.

� 2016 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction

The production of iron ore is largely used to meet the increasein the global demand for steel and pig iron. An estimated 1.5 billiontons of steel were produced globally in 2011 of which 683 milliontons was produced in China [1]. The increased rate in world steelproduction, driven largely by construction growth in China andMiddle East, has resulted in demand for high grade iron ore. Theescalating economic growth within these regions has resulted inthe exploration of more mineral ore deposits. The conventionalmethod for processing iron ore is by crushing the run of mine(ROM) material to <40 mm size fraction followed by scrubbingand/or wet screening at 10 mm to generate �40+10 mm fraction[2]. The �10+0.15 and �0.15 mm size fractions are usually classi-fied as fines and slimes, respectively. The slimes generated havebeen traditionally regarded as waste and usually dumped intoslime ponds. The rejection of these slimes is considered a lossand additionally harmful to the environment. In many instances,most of these fines are generated from mechanised mining opera-tions with millions of tonnes reporting to tailing dumps in SouthAfrica. Therefore, given the unused value in these materials, alongwith the findings by Mohanty et al., where iron ore slimes arefound to have high aluminium content with valuable Fe grade in

ranges >50%, it was paramount to exploit alternative beneficiationtechniques to further increase the yields and quality of the finefractions of iron ore in South Africa [2].

Numerous magnetic separation techniques (dry or wet) havebeen developed over the years to meet the requirement of the min-eral processing industry for the concentration of different ores.This is based on parameters such as the magnetic susceptibility dif-ferences in particles, the generation of higher magnetic field andthe design of the separator [3–10]. In addition, researchers havealso used both wet high and low magnetic separators for treatingdifferent minerals possessing different magnetic properties [11].In this research study, a new magnetic separation technique asreported in the ASIA Miner report and developed in China, wasused for the beneficiation of low grade hematite ore [12]. Theequipment relies on its high intensity magnetic capability designedto attract materials with weakly magnetic attributes. It is com-posed of a corrosion resistant stainless steel matrixes, constitutingof about 12% to 18% Cr content. The higher the chromium content,the more resistant the matrixes are to corrosion. It also has a watercooling system passing between the coils, which aids in reducingheat generated during runs.

The equipment was designed based on magnetic jigging princi-ples similar to a SLon, where the pulsation mechanisms assist inimproving separation efficiency. This is achieved by agitating thepulp and keeping the particles loose in order to minimise particleentrapment thus creating more surfaces for collecting particles.

echnol

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Theoretically, this principle allows the separation of mixtures withsmall differences in density and small difference in magnetic sus-ceptibility. Through the application of this new technique, theextraction of valuable particles from previously discarded finesand slimes dumps which previously were found not to be cost-effectively viable for beneficiation, could become a feasible option.In addition, the fines generated during the mining of iron ore couldbe beneficiated further to generate direct reduce iron (DRI) feedmaterial while other minerals like coal, manganese and chromitefound with gangue minerals containing iron phases could also beseparated using this approach [13]. With all the aforementionedpositive attributes of this WHIMS technique and no data reportedusing the Longi magnetic separator in beneficiating South Africaniron ore, it needs to determine the separation capabilities of thisseparator based on an estimated 450 million tons of slimes gener-ated and dumped annually in South Africa. The research aims todetermine the optimum process conditions on the Sishen ironore for maximum achievable grade and recovery and to analysethe influence of variables on the material using a statisticalapproach.

2. Experimental

2.1. Material

A low grade iron ore material was acquired from Sishen Mine,Northern Cape in South Africa for the purpose of this study. Thematerial was received at �32+8 mm size fraction and was groundusing a high pressure grinding roll (HPGR) to generate sample<1.18 mm size fraction. The ground material was then blendedusing a combination of a riffle splitter and a rotary splitter to main-tain homogeneity and to obtain representative sub-samples. TheSEM-energy dispersive X ray spectroscopy (EDS) detector system

Fig. 1. BSE image from the �1.18 mm feed.

Table 1Particle size distribution and composition of the �1.18 mm feed material.

Sieve screen (lm) Mass (%) Cum mass (%)

+1180 0.06 0.06�1180+850 4.72 4.78�850+600 19.99 24.77�600+425 16.40 41.18�425+300 14.19 55.37�300+212 10.76 66.13�212+150 14.65 80.78�150+106 3.01 83.80�106+75 6.33 90.12�75+53 3.14 93.26�53 6.74 100

Head grade 100

Please cite this article in press as: Makhula MJ et al. Statistical analysis and co(2016), http://dx.doi.org/10.1016/j.ijmst.2016.05.052

and back scattered electron (BSE) images show that the sample(<1.18 mm) is predominantly Fe oxide in a form of hematite withsilicates as main gangue minerals as presented in Fig. 1, whilethe particle size distribution analyses on each of the sizes as shownin Table 1 was analysed for elemental composition using X ray flu-orescence (XRF). The result obtained from the sizing indicated thatthe majority of the mass is distributed within the 850 and 150 lmfraction. The remaining material was screened at 106 and 75 lmusing the Sweco vibrating sieve to generate �1000+106, �106+75 and �75 lm size fractions. A head grade was then determinedfrom the individual size fractions and was calculated to be 43.54%Fe, 14.49% SiO2 and 13.66% Al2O3. The sizing results showed anevenly distributed Fe grade, ranging between 41% Fe and 44% Fe.

2.2. Test procedures

A wet-high intensity magnetic separator (WHIMS), in a form ofLongi LGS 500, was used for this study. It is semi-continuous pilotscale equipment, constituting of a 500 mm diameter rotating rotorwith replaceable matrixes. It also consists of a collecting point forthe magnetic particles, a pulsating mechanism to keep particleloose from the matrix and the wash water system to wash offthe particles and keep the matrix clean. The throughput of the sep-arator ranges between 0.05 and 0.25 ton per hour, and slurry den-sity within 10% to 40% solids. For this study, each of the sizedmaterial was individually treated in 10 kg batches on the LongiLGS 500 WHIMS, and the effective separation performance of theseparator was determined by varying the following set parameters,i.e. pulp density, magnetic field intensity and pulsating frequency.The matrixes were set at a distance of 2 mm, rotor standard speedof 4 r/min, and constant wash water and feed rate. The pulp wasprepared at 20%, 25% and 30%, and allowed to be agitated for5 min before being fed into the separator. Varying magnetic fieldof 1000, 5500 and 10,000 G were tested, along with pulsating fre-quency of 6, 12 and 25.2 Hz. The pulsator assists in keeping parti-cles loose and prevents the clogging of the matrix as a result of theback and forth motion from the frequency converter. As the ringrotates, the attached magnetic particles were collected from thepulp and vigorously washed off into the concentrate holding plateand non-magnetic particles are released from the matrix into aseparate collector. For each test, three products were collected,i.e., the magnetic, middlings and non-magnetic, they were individ-ually filtered and oven dried at 105 �C. Once dried, all productswere blended, sub-sampled in preparation for chemical analyses.

3. Results and discussion

Three different size fractions (1000+106, �106+75 and�75 lm)of hematite ore were used and the influence of pulp density,

Passing (%) Grade (%)

Total Fe SiO2 Al2O3

100.00 41.43 15.10 15.2099.94 43.75 14.45 14.5095.22 44.63 13.80 13.1075.23 44.18 13.60 13.9058.82 44.15 13.40 13.8044.63 44.16 13.70 13.9033.87 43.62 14.40 13.6019.22 41.51 15.70 13.7016.20 41.51 17.10 13.409.88 40.30 18.60 13.606.74 40.43 17.60 13.90

43.54 14.49 13.66

ncentration of iron ore using Longi LGS 500 WHIMS. Int J Min Sci Technol


47.4145.58

52.10 51.06 51.7055.16 54.19

46.4848

56

64 Mass yield concentrate Fe gradeFe recovery

SiO2 grade

SiO recovery

Head grade: 43.52% Fe, 15.50 % SiO2

)

M.J. Makhula et al. / International Journal of Mining Science and Technology xxx (2016) xxx–xxx 3

magnetic field intensity and pulsation frequency was evaluated foreffective separation of the Longi LGS 500. The results from eachparameter are discussed in the sections below and the data fromthe product’s grade and yield validated by using analysis of vari-ance (ANOVA).

25.53

9.42 9.31 9.22

28.89 27.2824.40

0

8

16

24

32

40

20 25 30

Pulp density (%)

2

Gra

de /

mas

s yie

ld (%

Fig. 3. Effects of changes in pulp density for �106+75 lm size fraction.

11.29

36.0133.02

29.78

49.70 50.80 49.9044.22 42.64

37.24

10.43 11.30

24.72 24.64 24.06

0

8

16

24

32

40

48

56

64

20 25 30

Pulp density (%)


Mass yield concentrate Fe gradeFe recoverySiO 2 gradeSiO2 recovery

Gra

de /

mas

s yie

ld (%

)

Fig. 4. Effects of changes in pulp density for �75 lm size fraction.

62.45

56.3453.7556

64

Head grade: 44.75% Fe, 13.60 % SiO2Mass yield concentrate Fe gradeFe recovery

3.1. Effects of pulp density

As stated by Joseph, any variation in pulp density will alter thevelocity at which particles are introduced to the magnetic separa-tor and therefore may be expected to alter the process efficiencyduring separation [14]. As pulp density decreases below a thresh-old value, the pulp velocity increases, causing a rapid flow throughthe rotating rotor, thus reducing particle capture and recoverycapabilities of the magnetically induced particles. The pulp densityincreases above the known threshold value, the particles tend toovercrowd the matrix and reduce the recovery capability of thematrix [14]. In this study, the effect of varying pulp density wasinvestigated while the magnetic field and pulsation frequencywere kept constant at 2800 G and 12 Hz. The results were in agree-ment with the authors’ findings and were promising where com-paring mass yield concentrate and Fe grade was concerned. Itcould be that at a low pulp density of 20%, particles move freelywith less inter-particles forces. This eliminates formation of coag-ulate. Also, when the magnetic particles attached on the matrix,they were easily washed off the matrix to create more surface areafor incoming particles to attach which resulted in high mass yieldsconcentrates and Fe recoveries. As the pulp density increased from20% to 25% and 30%, there was a decrease in Fe recovery. This couldhave been as a result of increased overcrowding on the matrix. Insuch instances, there is a limited surface area for the incomingmagnetic particles to attach, thus reducing the overall Fe recovery.It can be noted that, with the decrease in the particle recovery, thequality of the product was not affected, remaining within the sameranges of 50% Fe to 52% Fe as shown in Figs. 2–4. This furtherproves the decrease in surface area was the main reason for thedecrease in overall mass yield concentrate and Fe recovery. Thiswas the trend in all three size fractions �1000+106, �106+75and �75 lm. Thus, for high Fe recoveries and relatively good Fegrades, the tests could be conducted at <30% pulp density.

12.34

45.0850.10 48.78 47.18

43.53 40.75

10.73 11.00 12.009.70

36.32

8

16

24

32

40

48

SiO2 gradeSiO2 recovery

Gra

de /

mas

s yie

ld (%

)

3.2. Effects of magnetic field strength

The principle of magnetism states that, the higher the magneticfield intensity, the higher the probability of a particle to be cap-tured [15]. In other words, the efficiency of a magnetic separatorfor effective removal of non-magnetic particles from magnetic par-ticles depends on the intensity and magnetic flux generated, along

47.48

39.1935.61

51.94 50.90 50.42

56.34

43.5340.75

8.53 10.71 10.50

29.43 30.1926.83

0

8

16

24

32

40

48

56

64

20 25 30

Pulp density (%)


Gra

de /

mas

s yie

ld (%

)

Mass yield concentrate Fe gradeFe recoverySiO2 gradeSiO2 recovery

Fig. 2. Effects of changes in pulp density for �1000+106 lm size fraction.

01000 5500 10000

Magnetic field intensity (Gauss)

Fig. 5. Effects of changes in magnetic field intensity for �1000+106 lm sizefraction.


with the matrix type used. The investigations on the effect of vary-ing the current to generate magnetic field intensity from 1000 to5500 and 10,000 G were conducted. The pulp density and pulsationfrequency were kept constant at 30% and 12 Hz respectively. Thevariation of the magnetic field intensity was shown to have a majoreffect on the quality of the product. From a separation efficiencypoint of view, an increase in magnetic field intensity had a positiveeffect on the mass yield concentrate and recovery. However, theincrease in magnetic field intensity had a negative effect on theproduct quality. This was noted for all three size fractions as shown



16.63

51.97

59.58

51.6047.47

40.80

18.80

56.42 56.92

10.11

17.18 17.2412.55

63.99

70.61

0

8

16

24

32

40

48

56

64

72

1000 5500 10000Magnetic field intensity (Gauss)


Gra

de /

mas

s yie

ld (%

)


Fig. 6. Effects of changes in magnetic field intensity for �106+75 lm size fraction.

8.91

29.71

45.7149.74 48.36 46.52

24.8528.81 30.28

11.40 11.00 11.907.29

23.93

38.55

1000 5500 10000

Magnetic field intensity (Gauss)


0

8

16

24

32

40

48

56

64

Gra

de /

mas

s yie

ld (%

)

Mass yield concentrate Fe gradeFe recovery

SiO2 gradeSiO2 recovery

Fig. 7. Effects of changes in magnetic field intensity for �75 lm size fraction.

16.15

27.59 27.65

50.25 50.1 52.30

18.40

31.44 31.81

10.51 10.14 9.116.01

21.1218.25


0

8

16

24

32

40

48

56

64

Gra

de /

mas

s yie

ld (%

)

6.5 19.5 25.2

Pulsation frequency (Hz)


Fig. 8. Effects of changes in pulsation frequency for �1000+106 lm size fraction.

19.9223.42 24.44

54.4 54.55 54.45

24.8528.81 30.28

10.19 10.97 10.6712.98

16.68 14.47

0

8

16

24

32

40

48

56

64

6.5 19.5 25.2Pulsation frequency (Hz)


Gra

de /

mas

s yie

ld (%

)


Fig. 9. Effects of changes in pulsation frequency for �106+75 lm size fraction.

18.25 19.04 20.91

48.3052.25

55.00

21.4224.91

29.19

10.83 10.41 9.2314.07 14.37 14.40

0

8

16

24

32

40

48

56

64

6.5 19.5 25.2

Pulsation frequency (Hz)


Gra

de /

mas

s yie

ld (%

)


Fig. 10. Effects of changes in pulsation frequency for �75 lm size fraction.


in Figs. 5–7, whereby the mass yield concentrate and SiO2 contentincreased with increase magnetic field intensity. It could have beenas a result of both the high and weakly susceptible particles werepulled towards the matrix’s surface area. At the same time, thisincrease in magnetic field intensity could have created enoughforce for the magnetic particles to form coagulates as they attachon the matrix. During this process, the finely sized non-magneticparticles mechanically entrapped are then released from the coag-ulates when the rotating rotor moved away from the highly mag-netised separating zone to where the magnetic field is lowest.These non-magnetic particles would have been released into themagnetic stream launder, thus increasing the mass yield to con-centrate, at the same time diluting the product grade.

Based on the results attained, it would appear that to achievehigh Fe recoveries, high magnetic field intensity of 10,000 G needsto be applied, however, this would compromise the product qualitydue to accumulated diluting gangue minerals. At such magneticfield intensity, this process could be used as a primary rejectionstage for downstream cleaning stages. Alternatively, to achieve areasonably good Fe grade of >50% Fe with <10% SiO2, an intensityof 1000 G needs to be applied, but this would compromise theoverall Fe recoveries to <20%. The results do show that Longi LGS500 WHIMS has matrix capabilities to generate enough force tofacilitate particle capture.

3.3. Effects of pulsation frequency

In order to reduce particle entrapment, clogging of the matrixand to improve product quality, the pulsation mechanism of theLongi LGS 500 magnetic separator was used. Its effect is such that,as the pulsating frequency increases, the competing forces


(hydrodynamic and drag forces) acting upon the non-magneticparticles increase. This effect prevents entrapment of fine sizednon-magnetic particles within the magnetic coagulates [3]. Thecurrent investigations were conducted by varying the pulsationfrequency from 6.5 to 19.5 and 25.2 Hz, while magnetic field inten-sity and pulp density were kept constant at 2800 G and 30% pulpdensity. The results from the three size fractions treated show thatthe pulsation frequency has a positive effect on the overall qualityof the product. High mass yields concentrate with a maximumachievable Fe grade of 55% Fe (Figs. 8–10) with low gangue con-tents were achieved in all three size fractions. It could be that asthe pulsation frequency increased, the pulp was agitated resulting



Table 2Independent variables and (33) full factorial design.

Level X1 (%) X2 (G) X3 (Hz)

(a) VariableLow 20 1000 6.5Medium 25 5500 19.5High 30 10,000 25.2

Input X1 (%) X2 (G) X3 (Hz)

(b) Full factorial design 331 0.20 2800 12.02 0.25 2800 12.03 0.30 2800 12.01 0.30 1000 12.02 0.30 5500 12.03 0.30 10,000 12.01 0.30 2800 6.52 0.30 2800 19.53 0.30 2800 25.2

Table 3Analysis of variance (ANOVA) outputs on the interaction of variables.

Group Count SOS Average Variance

(a) Anova output of mass yield concentrates (%)Column 1: X1 27 1807.06 66.93 133.61Column 2: X2 27 508.63 18.84 167.33Column 3: X3 27 86.59 3.21 4.55Column 4: X1X2 27 81.23 3.01 40.83Column 5: X1X3 27 46.24 1.71 1.86Column 6: X2X3 27 151.71 5.62 78.89Column 7: X1X2X3 27 144.69 5.36 78.16

(b) ANOVA output of Fe grade (%)Column 1: X1 27 26.59 0.98 21.80Column 2: X2 27 74.97 2.78 9.78Column 3: X3 27 87.23 3.23 4.32Column 4: X1X2 27 263.34 9.75 51.09Column 5: X1X3 27 79.27 2.94 1.32Column 6: X2X3 27 407.59 15.10 95.81Column 7: X1X2X3 27 391.92 14.52 102.82


in an upwards and downward movements of particles within theseparation zone. This created an adequate distance between parti-cle and rotor together with the number of times the particles inter-acted with the rotor. During such process, selectivity is increasedand eliminating the entrapment of the non-magnetic particles,hence improved mass yield concentrates as the pulsation fre-quency was increased.

Therefore, the high pulsation frequency is necessary for releas-ing non-magnetic particles from the matrix and thereby for keep-ing the matrix clean and facilitating good quality products. It wasalso evident that a high pulsation frequency of 25.2 Hz, 30% pulpdensity and 2800 G were the optimum conditions for achievinggood Fe grade and overall product recovery.

Table 4Analysis of variance (ANOVA) for linear model of Fe ore mass yield and grade.

Source of variation SOS df M

(a) Output data for mass yield concentrateBetween groups 12261.45 6.00 2Within groups 13136.10 182.00 7Total 139748.54 188.00

(b) Output data for Fe gradeBetween groups 14533.46 6 2Within groups 7460.39 182 4Total 2199.85 188.0


3.4. Statistical analysis: analysis of variance (ANOVA)

The method of analysing data using analysis of variance(ANOVA) is widely used in mineral processing for evaluating thesignificance of the variables used during investigations [15,16].The ANOVA outputs were obtained from a Microsoft office, Excel2010 spreadsheet, using data from twenty-seven (27) test runson the iron material at three size fractions. The test runs werebased on the full factorial design 33 following an equation shownbelow.

N ¼ 2 z ð1Þ

where N is the number of investigations; and z the number ofvariables.

The effects of the three variables at three levels (Table 2) wereinvestigated namely: (X1) pulp density (%), (X2) magnetic fieldintensity (G) and (X3) pulsation frequency (Hz). The estimatedcoefficients from the mathematical model together with theANOVA outputs are discussed in Sections 3.5 and 3.6 below.

3.5. Interaction effects

Tables 3 and 4 show ANOVA outputs and the discussion werebased on the null hypothesis, which makes comparison of themean between groups and mean within a group. The hypothesissuggests that there is no difference between the two means, i.e.effects of the variables are the same and the decisions on whetherto accept or reject the hypothesis were based on the ratio betweenF value and F critical. If the F value is <F critical, then the nullhypothesis will be accepted, and the opposite is true. If F value>F critical, the null hypothesis will be rejected. The results showthat of the three variables, X2 with the largest positive sum of allsquare value in the mass yield concentrate, followed by X3. X3

has a more significant effect while X1 reported a negative sum ofsquare value but reported as an absolute value, suggesting the leasteffect. Thus, as the parameters X2 and X3 increased, the mass yieldconcentrate and Fe grade also increased. The opposite was true forX1, whereby an increase in parameters had a negative impact onthe mass yield concentrates with Fe grade remaining relativelywithin the same ranges. The order of significant effect wasX2 > X3 > X1 and X2X3 > X1X2 > X1X3 > X1X2X3.

To achieve good product quality using Longi LGS 500 for lowgrade hematite material at three size fractions, a balance betweenthe main parameters X2 and X3 would be required. The X2X3 wasshown to have the most effect compared to X1X2, X1X3 and themore complex X1X2X3, further supporting the fact that the twovariables were the main parameters for achieving optimum sepa-ration. Thus, a balance could be at a low magnetic field intensityallowing for recovery of the highly susceptible particles free ofthe gangue and at a high pulsation frequency ensuring that allthe non-magnetic particles are not attached to the matrix or evenentrapped within the non-selective coagulates.

S F value P-value F critical

1102.07 292.37 0.00 2.152.18

422.24 59.09 0 2.150.99



Table 5Regression coefficients from the actual and modelled data.

Size fraction (lm) Regression coefficient (R2)

(a) Mass yield concentrate (%)�1000+106 0.90�106+75 0.87�75 0.86

(b) Fe grade (%)�1000+106 0.84�106+75 0.84�75 0.96


Table summarises the ANOVA outputs for mass yield concen-trates and the grade of the Fe ore, from which the sum of allsquares (SOS), degree of freedom (df), mean square (MS), F value,probability (P) value and F critical were determined and conclu-sions drawn. The P value gives an indication of the significance ofvariables in predicting the responses to individual and interactiveeffects [16,17].

The results reported low P values at <0.05 indicating that themodel is significant at 95% confidence level. Based on these results,the variables were considered significant for the magnetic separa-tion process.

3.6. Mathematical model

The mathematical model used is a linear regression equation asshown in Eq. (2), to determine howwell the model fits to the actualdata. A Microsoft 2010 excel was used for determining this rela-tionship, mainly for mass yield concentrate and Fe grades. In gen-eral, the smaller the difference between the model and the actualvalues, the higher the regression coefficient i.e. R squared (R2),and the better the fit and closer to 100%.

Y ¼ ao þ a1X1 þ a2X2 þ a3X3 þ a4X1X2 þ a5X1X3 þ a6X2X3

þ a7X1X2X3 ð2Þwhere Y is the Fe grade or mass yield for the magnetic stream; and Xthe independent variable.

Table 5 shows correlations between the modelled outputs andthe actual values for the mass yield and the Fe grade. The resultsobtained further confirmed that X2 reported the highest positivevalues, indicating that it has the most significant effect. The X2X3

interaction was found to have contributed the most positive valueto the modelled value. The responses reported coefficients of 0.90,0.87, and 0.86 for mass yields concentrates and 0.84, 0.84, 0.96 forFe grade �1000+106, �106+75 and �75 lm fractions respectively,further suggesting the significance of the model. The authors Jogle-kar and May suggested a good R2 fit should at least be 0.80 [18].The results could be further supported by the results attained byAziz et al., who reported R2 of 0.93 for manganese recovery and0.94 for iron recovery [19]. Again the result by Tripathy et al., theR2 was reported at 0.94 for chromite grade and 0.93 for chromiterecovery [20].

3.7. Summary

The WHIMS investigations were conducted on three size frac-tions constituting of slightly different mineral Fe and SiO2 associa-tions. The results showed that the Longi LGS 500 possesses greatcapabilities for beneficiating the material, even at wide size ranges,for example the �75 lm size fraction reported up to 55%. The anal-ysis of variance together with the regression model was applied tovalidate the effects of the three variables investigated. From themodel outputs, the null hypothesis qualified to be rejected indicat-ing that the effects of the parameters were significant to the mass


yield concentrate and Fe grade responses, particularly magneticfield intensity and pulsation frequency. In addition, the regressioncoefficients from the modelled and actual values were in good cor-relation and were reported to be in the range of 0.84 to 0.96.

4. Conclusions

The effects of varying the pulp solids, magnetic field intensityand pulsation frequency provide detailed beneficiation capabilitiesof the newly developed Longi LGS 500 WHIMS on a low grade ironore material prepared to three different size fractions. From theresearch investigations, the following conclusions were drawn:

(1) It was observed that the Longi LGS 500 is potentially goodfor beneficiating low grade iron ore fines, and the back scat-tered electron (BSE) images showed that the ore is predom-inantly Fe oxide in a form of hematite with silicates as maingangue minerals.

(2) It was noted that the increase in pulp density from 20% to25% and 30% had a negative effect on the mass yield of con-centrate. At pulp solids >20%, the matrix was overloadedresulting in the concentrate mass yields concentrate andFe recoveries decreasing with no significant effects on theFe grade.

(3) The changes in magnetic intensity from 1000 to 10,000 Gincreased the mass yield of the concentrates, while the pul-sation mechanism, on the other hand, positively affected theoverall quality of the product, more so on the �75 lm sizefraction. An increase from 6.5 to 19.5 and 25.5 Hz showedan increase in both the mass yield concentrates and Fegrade.

(4) The interactions between parameters were shown to beessential, and most notable was between X2X3 having themost effect, followed by X1X3 then X1X2X3. These results sup-ported the fact that of the two variables investigated, the X2

and the X3 had a major individual effect on this particulariron sample.

(5) The optimum conditions for iron ore could be achieved at20%, 2800 G and a pulsation of 25.2 Hz.

Acknowledgments

The author would like to express gratitude to NRF SARChI CleanCoal Technology, Mintek – South Africa and the University of theWitwatersrand for making funds available for the research studyand all those assisted during the investigations.

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